Thin sheets of ceramic material are useful as electrical insulators and supports for thin film electronic circuits and other applications. The forming of such sheets before firing is difficult, which results in a low yield of finished product, because the sheets tend to crack after casting.
Various methods have been employed for providing crack-free sheets before firing. (The material after casting and drying but before firing is commonly referred to as tape.) Such methods include nearly saturating the drying air with solvent vapor immediately after casting and using a support film of material such as cellulose acetate, so that the film will contract along with the shrinking tape during drying. These methods are difficult to reproduce, and they impose limitations on the range of materials and conditions that can be used. The prior art methodology is fully disclosed in the following references: U.S. Pat. No. 2,582,993 to HOWATT, U.S. Pat. No. 3,698,923 to STETSON and U.S. Pat. No. 3,780,150 to STETSON, as well as in Shanefield, et al. "Fine Grained Alumina Substrate: I, the Manufacturing Process, " American Ceramic Society Bulletin, vol. 53, pp. 416-420, May 1974, Shanefield, "Tape Casting for Forming Advanced Ceramics," in "Encyclopedia of Materials Science and Engineering,", edited by M. B. Bever, Pergamon Press, 1986 and J. C. Williams, "Doctor-Blade Process," in "Treatise on Materials Science and Technology," edited by F. Y. Wang, Academic Press, 1976. The disclosures of these references are incorporated herein by reference